Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$123.48	6.845%	$131.9322	$131.93	$131.95	$131.90
Purchase #2	$212.98	10.718%	$235.8072	$235.81	$235.80	$235.80
Purchase #3	$117.74	4.831%	$123.428	$123.43	$123.45	$123.40
Purchase #4	$35.29	7.321%	$37.8736	$37.87	$37.85	$37.90
Purchase #5	$37.39	4.350%	$39.0165	$39.02	$39.00	$39.00
Purchase #6	$207.35	12.768%	$233.8244	$233.82	$233.80	$233.80
Purchase #7	$19.72	7.612%	$21.2211	$21.22	$21.20	$21.20
7 purchase totals =	$753.95		$823.1030	$823.10	$823.05	$823.00